1. Field of the Invention
The present invention relates to a communication method and apparatus, which corrects, at a receiving side, a data error caused by a communication path or a storage medium in a digital communication system and a digital storage system.
2. Description of the Related Art
Decoding methods of error-correcting codes can be classified into hard decision decoding methods and soft decision decoding methods. A hard decision decoding method is a method of performing error correction for a digital sequence obtained by hard-deciding a reception signal to "0" and "1". Since the arrangement of a decoder is simple, this method is widely used for various media such as a CD (Compact Disk).
On the other hand, in a soft decision decoding method, an analog weight indicating a probability of a digital sequence obtained by soft-deciding a reception signal is calculated in addition to the digital sequence, and error correction is performed by utilizing the analog weight. For this reason, this method sufficiently brings out the capability of error-correcting codes, and improves the S/N ratio by about 2 to 3 dB as compared to the hard decision decoding method.
A GMD (Generalized Minimum Distance) decoding method to be described below is one of the soft decision decoding methods, and is known as a decoding method which almost performs maximum likelihood decoding using an analog weight. If the minimum distance of codes is represented by d, the conventional GMD decoding corrects a maximum of (d-1) errors, and realizes error correction about twice the correction capability obtained by a single hard decision decoding cycle.
However, since the GMD decoding requires a maximum of (d-1)/2 hard decision decoding cycles, a larger computational complexity is required than the hard decision decoding method which requires only a single decoding cycle, resulting in a large calculation circuit scale and a long calculation time.